Newman et al : Variability in the population structure of Lutjanus adetii and L quinquelineatus 



325 



Doherty and Fowler, 1994b). Further, the suggestion 

 that recruitment variability is a major factor influenc- 

 ing both the distribution and local densities of coral 

 reef fishes has been recognized for a number of years 

 (Williams, 1980; Doherty, 1981, 1983, 1991; Victor, 1983; 

 reviews of Doherty and Williams, 1988). Subsequently, 

 Doherty and Fowler ( 1994b) have shown that for the 

 common tropical damselfish Pomaeentrus moluccensis, 

 age structures from individual reefs have preserved ma- 

 jor temporal variations in the recruitment patterns over 

 at least 10 years, providing empirical evidence of a 

 strong effect of recruitment history on subsequent year- 

 class strength. It is therefore conceivable that the vari- 

 ous age structures of both lutjanid species among reefs 

 is a consequence both of variability in recruitment at 

 the localized scale of individual reefs and of good re- 

 cruitment years persisting in the age structure of popu- 

 lations over time. 



Estimates of the rate of natural mortality in fish 

 populations are essential to fishery management (see 



Ricker, 1975; Gulland, 1983; and Russ, 1991). The 

 mortality rate for L. adetii was significantly differ- 

 ent among reefs, although these differences were 

 small. The mortality rates for this species in general 

 were low and the rates of survivorship were corre- 

 spondingly high. Mortality rates for L. quinque- 

 lineatus were not obtainable from all reefs owing to 

 either the persistence of strong year-class modes, 

 (possibly to nonconstant mortality rates at a num- 

 ber of reefs (although these were not detected among 

 years at Lodestone Reef), or differential mortality of 

 cohorts (as opposed to interannual variability in 

 mean [cross-cohort] mortality rates). The results ob- 

 served here suggest that interannual variation in 

 recruitment may be retained in the age structure at 

 each reef as found for P. moluccensis (Doherty and 

 Fowler, 1994b). Mortality rates derived with the 

 catch-curve method of Beverton and Holt ( 1957 ) and 

 Ricker ( 1975) are based on the assumption that re- 

 cruitment is constant in the population under con- 



